This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The structure of the MATalpha2/MCM1/DNA complex has been solved to 2.25 angstroms previously (Tan S., Richmond T., Nature (1998) 391, p660-666). The preliminary structure has revealed an unusual conformation of the arm domain of MATalpha2 (residues 112-130 which links the MATalpha2 homeodomain to the MCM1 binding pocket). In one copy (called MATalpha2-cis)this region forms two anti-paralell beta sheets conformation while in the other (MATalpha2-trans) copy, the region forms a alpha helix (from residues 121-128). Their are two reasons for the different conformation which are (1) the spaciing between the MCM1-binding pocket and the MATalpha2 homeodomain are different and (2) the MATalpha2-trans makes a contact with a symmetry related copy of MCM1 in which the bending angle is altered by 90 degrees. We have cocrystallized MATalpha2 and MCM1 with new substrates that have an altered spacing between the MATalpha2 homeodomain and the MCM1 binding pocket. Our crystals diffract weakly at our home source xrays and are often thin in one dimension (typically-.2x.15x.02). We are looking for diffraction improvement so that the structure could be solved at a synchotron source. Our plan is to collect diffraction data at higher resolution. If high enough resolution is obtained, we should be able to use the data to solve the structure by molecular replacement techniques. We would also like to test crystals of MATalpha1/MCM1/DNA and Dot1/nucleosomes which previously do not yeild diffraction on our home source xrays.